2nd Day in a Row of Skyrocketing H2S for Mon Valley, 5th Exceedance of PA 24-Hour Standard in 6 Days

Updated: Oct 13

UPDATE: Poor air quality is expected to continue in the Mon Valley. While the Allegheny County Health Department did not address the most recent bout of elevated H2S concentrations, it did issue a Mon Valley Air Pollution Watch at 6:43 p.m. Monday. The message was shared via the Allegheny Alerts system and social media:




An exceedance of Pennsylvania’s 24-hour standard for hydrogen sulfide (H2S) is guaranteed today thanks to exceptionally high levels of the pollutant this morning at the Allegheny County Health Department’s air quality monitor in Liberty Borough - the second day in a row the Mon Valley has been inundated with industrial stench.


In fact, today marks the fifth such exceedance at the Liberty monitor in the past six days. One of those six days includes a dreadful episode last week when concentrations of H2S exceeded the state’s one-hour standard for the first time since 2015.


For perspective, H2S levels exceeding the state 1-hour standard have only occurred nine times in the past 20 years, according to ACHD monitor data.


The rarely-seen, sky-high H2S levels resulted in GASP filing a formal air quality complaint with the county health department asking ACHD to consider updating residents through a public alert.


Our concern is that exposure to the levels of H2S we see in the Mon Valley can cause irritation to the eyes, nose, or throat as well as headaches, poor memory, tiredness, and balance problems. It may also cause difficulty in breathing for some asthmatics, according to the Agency for Toxic Substances and Disease Registry.

As for the source of the Mon Valley’s H2S problem, a recent examination of H2S issues in the area suggests it’s none other than U.S. Steel: A 31-page study ACHD released this past spring found that years’ worth of H2S exceedances in the Mon Valley “can be attributed entirely” to emissions from its Clairton Coke Works operations. Just days later, the department issued a $1.8 million enforcement order against U.S. Steel over the H2S emissions issue. The company appealed the order and the case is ongoing.

While GASP appreciates that the department issued public updates about the elevated levels of H2S at the Liberty monitor, we were disappointed that those messages blamed the weather instead of the source of the pollution.

“Yes, there was an inversion overnight last week when H2S levels hit their highest level in seven years, and yes, inversions contribute to poor air quality, but ACHD’s own analysis shows we average around 150 days with an inversion per year,” said GASP staff attorney Ned Mulcahy. “Given the regularity of inversions and the stark scarcity of one-hour H2S exceedances, I think the ‘inversion’ explanation ACHD offered is incomplete at best.”

Atmospheric science aside, the outreach also struck us as not appreciating the human impact of the high H2S levels.

“We found it extremely troubling that our public health department failed to include any information about how hydrogen sulfide can impact public health, instead describing the issue as merely a nuisance,” GASP Executive Director Patrick Campbell said. “It also failed to communicate what - if anything - the department is doing to get to the root of the problem.”

He continued:

“When people wake up, go outside, and are assaulted by stench and unhealthy air quality they need to be able to rely on the people who are charged with protecting their health to let them know what’s happening to cause it and what steps they can take to mitigate their exposure. Right now they just aren’t getting that level of service and it’s shameful.”

GASP again calls on ACHD for a robust public update shared through the Allegheny Alerts system and communicated to local news media to ensure the information is shared as broadly as possible.

We continue to follow this issue - and monitor data - closely and will keep you posted.



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